Track circuit



Jul 19, 1938. F, X; REES 2,123,965

TRACK CIRCUIT Filed Aug. 2]., 1935 FIG. 1.

ATTORNEY Patented July 19, 1938 oFFice TRACK CIRCUIT Frank X. Rees,Albany, N. Y., assignor to General Railway Signal Company, Rochester, N.Y.

Application August 21, 1936, Serial No. 97,204

3 Claims.

This invention relates to improvements in the well-known track circuitsfor railroads, and more particularly to'alternating current trackcircuits. .The primary object .of the presentinvention is to improve theshunting operation of the usual track re lay .of alternating currenttrack circuits under varying conditions of rail surface and ballastresistance.

This invention is in the nature of a variation or modification forcarrying out the principles and mode of operation characteristic. of thetrack circuit organization disclosed and claimed in my prior applicationSer. No. 24,074, filed May 29, 1935, and no claim is made herein to theinvention disclosed in said prior application.

The reliable operation .of the usual track circult depends uponestablishing a conducting path of low resistance through the axles andwheels of a car or train; and the weight of the equipment and conditionof the rail surface are important factors affecting theresistance of awheel shunt. For example, where the track rails of ,sidings, crossovers,and the like areinfrequently used, a coating of rust, usually an .ironoxide, accumulates on the rail surface, and makes any wheel shunt ofhigh resistance for the relatively small inter-rail voltages commonlyemployed; and even where train movement. is 30, frequent and the railsurface appears clean, a coating or film in the form of .an oxide ofsilicon, or some other stable. compound, is present on the rail surface,and offers a relatively high effective resistance for low voltages. Itis found that :5 these various coatings or films on the rail surface,apparently because they are in the nature of .a stable chemical compoundor composition, will break down and become a low resistance conductingpath upon the. application of suffii0= cient voltage, which may betermed an ionization voltage.

Generally speaking, and Without attempting to define the exact natureand scope of the invention, it is proposed to provide a transformer ofspecial construction, conveniently termed a peaker voltage transformerfor supplying current to the ordinary alternating current track circuit,so that relatively high peak voltages of short duration are obtained,'ascompared with the usual sine wave shape of voltage required for theaverage orefiective relay energizing current, thereby serving to breakdown or ionize the film or coating on the rail surface and render moreeffective the shunting action of the wheels and 55. axles of a train ortrains.

Various characteristic features, attributes, and advantages of theinvention will be in part apparent, and in part pointed out, as thedescription progresses.

The accompanying drawing illustrates in a simplified and diagrammatic'manner certain specific embodiments of the invention, the parts andcircuits being shown more with the view of facilitating an explanationand understanding of the invention, than for the purpose of showing indetail the structural organizations to be employed in practice.

In the drawing, Fig. 1 shows one track circuit section equipped with analternating current track circuit in accordance with this invention;Fig. 2 is a fragmentary View illustrating a modified arrangementincluding a single element relay with the usual impedance bond; and Fig.3 is an explanatory diagram of a theoretical relation of the primary andsecondary fluxes and secondary voltage of a peaker voltage transformercharacteristic of the invention.

Referring to Fig. 1, it is assumed that the track rails l of the tracksection shown will be bonded together in the usual way, with insulated.joints 2 in both track rails to define the ends of the track section. Atone end of the track section, preferably the entering end, an.alternating current track relay T of the .usual type and constructionis connected across the track rails I. As illustrated, this track relayT is of the usual two-element or polyphase type, having a track phasewinding 3 connected across the track rails and a local winding 4connected to the usual transformer 5 energized from an alternatingcurrent line 6, which in turn is energized from a generator G, orequivalent source, usually of a commercial frequency, such as 60 cycles.The track relay '1 may be a single element relay of the vane or rotortype, or in fact a relay of any one of the various types well known inthe art and used for alternating current track circuits as for instanceshown in Fig. 2.

In accordance with this invention, alternating current is supplied .tothe other end of the track section from a peaker voltage transformer PTof special construction. This transformer PT is shown diagrammatically,and comprises a primary 1 connected to the A. C. line circuit 6, and asecondary winding .8 connected across the track rails I in series withthe usual limiting resistance or reactance 9. In the type of peakervoltage transformer PT contemplated, the core for the secondary 8 has asmall magnetic section as compared with the core for the primary 1, andis also provided with a magnetic shunting core l0 of appropriate sectionwith a reluctance gap.

The purpose of this peaker voltage transformer PT is to provide highpeaked secondary voltage waves of short duration. Referring to Fig. 3,if the primary flux is represented by the sign curve A, the parts are soproportioned that the secondary flux corresponds approximately with thatindicated by the dot-and-dash curve B, and the secondary voltages arethose illustrated by the curve C. These curves of Fig. 3 are merelyillustrative of the principles and operation, and are not intended toshow quantitative values or relations. These characteristics areobtained by proportioning the cross section of the core for thesecondary winding 8 so that it becomes substantially saturated with alow flux density, the primary flux also passing in part through theshunting cores I0 and reluctance air-gap.

With such a peaker voltage transformer PT producing secondary voltagesas indicated by the curve C in Fig. 3, it is apparent that the maximumor peak Voltage which may be applied across the track rails to producean average or efi'ective relay energizing current, is much greater thanwith the ordinary sine wave of voltage commonly employed withalternating current track circuits. According to the principles of thisinvention, it is contemplated that these maximum or peak voltages willserve to break down or ionize the rail film and render the wheel shunteffective to conduct current at a lower inter-rail potential. These peakvoltages for breaking down rail film are repeatedly applied so as to beeffective as the wheels move to different spots on the track rails.

The track circuit organization of this inven tion may be advantageouslyemployed with double rail track circuits for electric propulsion roads,where impedance bonds are used, as illustrated in Fig. 2. With such anarrangement, the impedance of the bond is materially increased by theuse of the time-spaced peaked voltages obtained from the peaker voltagetransformer PT, as compared with the impedance of an equivalent coresection and number of turns excited with alternating current of the sinewave form. Consequently, the desired impedance across the bond toprovide proper excitation of the track relay T may be obtained by use ofthis invention by fewer turns, thereby reducing the cost of the bond andlowering its resistance to the propulsion current.

One important characteristic of this invention is that it assuresreliable shunting of the ordinary track circuit under unfavorableconditions of rail surface, weight of equipment, and ballast conditions.This desirable characteristic is due to the application of high peakedvoltages to break down the film or coating on the track rails, therebyassuring a shunting effect of the wheels and axles of a car or trainunder conditions where a lower voltage would be insufiicient.

The resistance of the wheel contact is found to vary greatly with theconditions of the rail surface and the weight of the equipment; and itappears that in many cases voltages much higher than the relativelysmall voltages, of about 2 volts normally employed for track circuitsare necessary to break down the resistance of the wheel contact to apoint where ionization and actual shunting of the track relay takesplace. The peak voltages provided by this invention, which are manytimes those commonly used in track circuits, apparently break down theresistance at the wheel contact by an ionization effect, and enableeffective shunting with dirty or rusty track rails and light-weightequipment in a manner not obtainable with the ordinary track circuitarrangement.

In this connection, it will be noted that the peak voltages areperiodically applied at frequent intervals and are available to breakdown the resistance of the wheel contact, as the car or train movesalong the track and its wheels contact with successive points on therails, and with the resistance once broken down it will remain of lowvalue until the train has left and an opportunity for soiling andoxidization of the rail surface has been presented.

The particular embodiments of the invention shown and described aremerely illustrative; and various adaptations, modifications, andadditions may be employed, without departing from the principles andmode of operation of the invention.

What I claim is:-

1. In an alternating current track circuit for railroads, thecombination with a section of railway track, a polyphase alternatingcurrent relay having two windings one connected across the track railsat one end of said section and the' other connected to a source ofsubstantially sinewave alternating current, a peaker voltage transformerfor changing a substantially sinewave alternating current voltage to avery peaked alternating current voltage comprising a core structure forvery loosely inductively coupling a primary winding and a secondarywinding wound thereon, said core structure also including a leakagemagnetic path for passing magnetic flux linking only said primaryWinding, and means for connecting said primary winding to said sourceand connecting said secondary winding across the track rails at theother end of said section, whereby the winding of said relay connectedacross the track rails is energized by a voltage which has a high ratioof'maximum to average value so that the voltage peaks of the alternatingcurrent voltage may act to break down the film resistance existingbetween wheels and rails to cause more effective wheel shunting withoutsupplying suflicient effective current to maintain said relay energizedduring the presence of a train.

2. In a track circuit for railway signalling systems, the combinationwith a section of railway track isolated from adjacent track sections byinsulating joints, an alternating current track relay connected acrossthe track rails at one end of said section and of a construction toassume an energized condition when an alternating current of a certaineffective value derived from a source of substantially sinewave form andof a certain voltage is connected across the rails at the opposite endof said section but assumes a deenergized condition upon entrance of atrain into said section, and a peaker voltage transformer fortransforming sinewave form alternating voltage into a peaked alternatingvoltage connected between a source of alternating current ofsubstantially sinewave form and said opposite end of said section tosupply alternating voltage of peaked wave form to said opposite endhaving a maximum value which is much greater than the maximum voltage ofsaid certain alternating voltage but supplies a current of only saidcertain effective value to said relay, whereby a high ratio of maximumto effective track circuit voltage is established in the track circuitso that the high voltage peaks of the alternating voltage may act tobreak down the film resistance existing between wheels and rails tocause more effective wheel shunting without supplying sufficientefiective current to maintain said relay energized during the presenceof a train.

3. A track circuit for railway tracks in which due to atmosphericconditions a high resistance film forms on the track rails, thecombination with a section of railway track isolated from adjacent tracksections by insulating joints, a twoelement alternating current trackrelay having its track circuit element connected across the track railsat one end of said section and having its local element connected to asource of substantially sinewave form alternating current, a seriesimpedance, and a peaker transformer energized from said source andsupplying peaked wave form alternating voltage to the other end of saidsection through said series impedance to supply peaked alternatingcurrent to the track element of said relay, said peaker transformertransforming said alternating voltage of substantially sinewave forminto a peaked Wave form voltage which has a very high maximum voltagefor each unit of efiective voltage as compared with the maximum voltageof sinewave form of unity effective value, whereby a high ratio ofmaximum to effective track circuit voltage is established in the trackcircuit so that the high voltage peaks of the alternating voltage mayact to ionize the film and break down the resistance existing betweenwheels and rails to cause more efiective wheel shunting withoutsupplying suflicient effective current in the track element of saidrelay to maintain said relay energized during the presence of a train.

FRANK X. REES.

